// Copyright Howard Hinnant 2007-2010. Distributed under the Boost
// Software License, Version 1.0. (see http://www.boost.org/LICENSE_1_0.txt)

#ifndef TING_SHARED_MUTEX_HPP
#define TING_SHARED_MUTEX_HPP

/*

<shared_mutex> synopsis

namespace ting
{

class shared_mutex
{
public:

    shared_mutex();
    ~shared_mutex();

    shared_mutex(const shared_mutex&) = delete;
    shared_mutex& operator=(const shared_mutex&) = delete;

    // Exclusive ownership

    void lock();
    bool try_lock();
    template <class Rep, class Period>
        bool try_lock_for(const std::chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
        bool
        try_lock_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock();

    // Shared ownership

    void lock_shared();
    bool try_lock_shared();
    template <class Rep, class Period>
        bool
        try_lock_shared_for(const std::chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
        bool
        try_lock_shared_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock_shared();
};

template <class Mutex>
class shared_lock
{
public:
    typedef Mutex mutex_type;

    // Shared locking

    shared_lock();
    explicit shared_lock(mutex_type& m);
    shared_lock(mutex_type& m, std::defer_lock_t);
    shared_lock(mutex_type& m, std::try_to_lock_t);
    shared_lock(mutex_type& m, std::adopt_lock_t);
    template <class Clock, class Duration>
        shared_lock(mutex_type& m,
                    const std::chrono::time_point<Clock, Duration>& abs_time);
    template <class Rep, class Period>
        shared_lock(mutex_type& m,
                    const std::chrono::duration<Rep, Period>& rel_time);
    ~shared_lock();

    shared_lock(shared_lock const&) = delete;
    shared_lock& operator=(shared_lock const&) = delete;

    shared_lock(shared_lock&& u);
    shared_lock& operator=(shared_lock&& u);

    void lock();
    bool try_lock();
    template <class Rep, class Period>
        bool try_lock_for(const std::chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
        bool
        try_lock_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock();

    // Conversion from exclusive locking

    explicit shared_lock(std::unique_lock<mutex_type>&& u);

    // Setters

    void swap(shared_lock& u);
    mutex_type* release();

    // Getters

    bool owns_lock() const;
    explicit operator bool () const;
    mutex_type* mutex() const;
};

template <class Mutex>
    void swap(shared_lock<Mutex>&  x, shared_lock<Mutex>&  y);

}  // ting

*/

#include <mutex>
#include <condition_variable>
#include <chrono>
#include <climits>
#include <system_error>

namespace ting {

class shared_mutex
{
    typedef std::mutex              mutex_t;
    typedef std::condition_variable cond_t;
    typedef unsigned                count_t;

    mutex_t mut_;
    cond_t  gate1_;
    cond_t  gate2_;
    count_t state_;

    static const count_t write_entered_ = 1U << (sizeof(count_t)*CHAR_BIT - 1);
    static const count_t n_readers_ = ~write_entered_;

public:
    shared_mutex();
    ~shared_mutex();

// Exclusive ownership

    void lock();
    bool try_lock();
    template <class Rep, class Period>
        bool try_lock_for(const std::chrono::duration<Rep, Period>& rel_time)
        {
            return try_lock_until(std::chrono::steady_clock::now() + rel_time);
        }
    template <class Clock, class Duration>
        bool
        try_lock_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock();

// Shared ownership

    void lock_shared();
    bool try_lock_shared();
    template <class Rep, class Period>
        bool
        try_lock_shared_for(const std::chrono::duration<Rep, Period>& rel_time)
        {
            return try_lock_shared_until(std::chrono::steady_clock::now() +
                                         rel_time);
        }
    template <class Clock, class Duration>
        bool
        try_lock_shared_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock_shared();

private:
    shared_mutex(const shared_mutex&);
    shared_mutex& operator=(const shared_mutex&);
};

template <class Clock, class Duration>
bool
shared_mutex::try_lock_until(
                       const std::chrono::time_point<Clock, Duration>& abs_time)
{
    std::unique_lock<mutex_t> lk(mut_);
    if (state_ & write_entered_)
    {
        while (true)
        {
            std::cv_status status = gate1_.wait_until(lk, abs_time);
            if ((state_ & write_entered_) == 0)
                break;
            if (status == std::cv_status::timeout)
                return false;
        }
    }
    state_ |= write_entered_;
    if (state_ & n_readers_)
    {
        while (true)
        {
            std::cv_status status = gate2_.wait_until(lk, abs_time);
            if ((state_ & n_readers_) == 0)
                break;
            if (status == std::cv_status::timeout)
            {
                state_ &= ~write_entered_;
                return false;
            }
        }
    }
    return true;
}

template <class Clock, class Duration>
bool
shared_mutex::try_lock_shared_until(
                       const std::chrono::time_point<Clock, Duration>& abs_time)
{
    std::unique_lock<mutex_t> lk(mut_);
    if ((state_ & write_entered_) || (state_ & n_readers_) == n_readers_)
    {
        while (true)
        {
            std::cv_status status = gate1_.wait_until(lk, abs_time);
            if ((state_ & write_entered_) == 0 &&
                                             (state_ & n_readers_) < n_readers_)
                break;
            if (status == std::cv_status::timeout)
                return false;
        }
    }
    count_t num_readers = (state_ & n_readers_) + 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
    return true;
}

template <class Mutex>
class shared_lock
{
public:
    typedef Mutex mutex_type;

private:
    mutex_type* m_;
    bool owns_;

    struct __nat {int _;};

public:
    shared_lock()
        : m_(nullptr), owns_(false) {}

    explicit shared_lock(mutex_type& m)
        : m_(&m), owns_(true)
        {m_->lock_shared();}

    shared_lock(mutex_type& m, std::defer_lock_t)
        : m_(&m), owns_(false) {}

    shared_lock(mutex_type& m, std::try_to_lock_t)
        : m_(&m), owns_(m.try_lock_shared()) {}

    shared_lock(mutex_type& m, std::adopt_lock_t)
        : m_(&m), owns_(true) {}

    template <class Clock, class Duration>
        shared_lock(mutex_type& m,
                    const std::chrono::time_point<Clock, Duration>& abs_time)
        : m_(&m), owns_(m.try_lock_shared_until(abs_time)) {}
    template <class Rep, class Period>
        shared_lock(mutex_type& m,
                    const std::chrono::duration<Rep, Period>& rel_time)
        : m_(&m), owns_(m.try_lock_shared_for(rel_time)) {}

    ~shared_lock()
    {
        if (owns_)
            m_->unlock_shared();
    }

    shared_lock(shared_lock&& sl)
        : m_(sl.m_), owns_(sl.owns_)
        {sl.m_ = nullptr; sl.owns_ = false;}

    shared_lock& operator=(shared_lock&& sl)
    {
        if (owns_)
            m_->unlock_shared();
        m_ = sl.m_;
        owns_ = sl.owns_;
        sl.m_ = nullptr;
        sl.owns_ = false;
        return *this;
    }

    explicit shared_lock(std::unique_lock<mutex_type>&& ul)
        : m_(ul.mutex()), owns_(ul.owns_lock())
    {
        if (owns_)
            m_->unlock_and_lock_shared();
        ul.release();
    }

    void lock();
    bool try_lock();
    template <class Rep, class Period>
        bool try_lock_for(const std::chrono::duration<Rep, Period>& rel_time)
        {
            return try_lock_until(std::chrono::steady_clock::now() + rel_time);
        }
    template <class Clock, class Duration>
        bool
        try_lock_until(
                      const std::chrono::time_point<Clock, Duration>& abs_time);
    void unlock();

    void swap(shared_lock&& u)
    {
        std::swap(m_, u.m_);
        std::swap(owns_, u.owns_);
    }

    mutex_type* release()
    {
        mutex_type* r = m_;
        m_ = nullptr;
        owns_ = false;
        return r;
    }
    bool owns_lock() const {return owns_;}
    operator int __nat::* () const {return owns_ ? &__nat::_ : 0;}
    mutex_type* mutex() const {return m_;}

private:
    shared_lock(shared_lock const&);
    shared_lock& operator=(shared_lock const&);
};

inline
shared_mutex::shared_mutex()
    : state_(0)
{
}

inline
shared_mutex::~shared_mutex()
{
    std::lock_guard<mutex_t> _(mut_);
}

inline
void
shared_mutex::lock()
{
    std::unique_lock<mutex_t> lk(mut_);
    while (state_ & write_entered_)
        gate1_.wait(lk);
    state_ |= write_entered_;
    while (state_ & n_readers_)
        gate2_.wait(lk);
}

inline
bool
shared_mutex::try_lock()
{
    std::unique_lock<mutex_t> lk(mut_);
    if (state_ == 0)
    {
        state_ = write_entered_;
        return true;
    }
    return false;
}

inline
void
shared_mutex::unlock()
{
    std::lock_guard<mutex_t> _(mut_);
    state_ = 0;
    gate1_.notify_all();
}

inline
void
shared_mutex::lock_shared()
{
    std::unique_lock<mutex_t> lk(mut_);
    while ((state_ & write_entered_) || (state_ & n_readers_) == n_readers_)
        gate1_.wait(lk);
    count_t num_readers = (state_ & n_readers_) + 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
}

inline
bool
shared_mutex::try_lock_shared()
{
    std::unique_lock<mutex_t> lk(mut_);
    count_t num_readers = state_ & n_readers_;
    if (!(state_ & write_entered_) && num_readers != n_readers_)
    {
        ++num_readers;
        state_ &= ~n_readers_;
        state_ |= num_readers;
        return true;
    }
    return false;
}

inline
void
shared_mutex::unlock_shared()
{
    std::lock_guard<mutex_t> _(mut_);
    count_t num_readers = (state_ & n_readers_) - 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
    if (state_ & write_entered_)
    {
        if (num_readers == 0)
            gate2_.notify_one();
    }
    else
    {
        if (num_readers == n_readers_ - 1)
            gate1_.notify_one();
    }
}

template <class Mutex>
void
shared_lock<Mutex>::lock()
{
    if (m_ == nullptr)
        throw std::system_error(std::error_code(EPERM, std::system_category()),
                                    "shared_lock::lock: references null mutex");
    if (owns_)
        throw std::system_error(std::error_code(EDEADLK, std::system_category()),
                                           "shared_lock::lock: already locked");
    m_->lock_shared();
    owns_ = true;
}

template <class Mutex>
bool
shared_lock<Mutex>::try_lock()
{
    if (m_ == nullptr)
        throw std::system_error(std::error_code(EPERM, std::system_category()),
                                "shared_lock::try_lock: references null mutex");
    if (owns_)
        throw std::system_error(std::error_code(EDEADLK, std::system_category()),
                                       "shared_lock::try_lock: already locked");
    owns_ = m_->try_lock_shared();
    return owns_;
}

template <class Mutex>
template <class Clock, class Duration>
bool
shared_lock<Mutex>::try_lock_until(
                       const std::chrono::time_point<Clock, Duration>& abs_time)
{
    if (m_ == nullptr)
        throw std::system_error(std::error_code(EPERM, std::system_category()),
                          "shared_lock::try_lock_until: references null mutex");
    if (owns_)
        throw std::system_error(std::error_code(EDEADLK, std::system_category()),
                                 "shared_lock::try_lock_until: already locked");
    owns_ = m_->try_lock_shared_until(abs_time);
    return owns_;
}

template <class Mutex>
void
shared_lock<Mutex>::unlock()
{
    if (!owns_)
        throw std::system_error(std::error_code(EPERM, std::system_category()),
                                "shared_lock::unlock: not locked");
    m_->unlock_shared();
    owns_ = false;
}

template <class Mutex>
inline
void
swap(shared_lock<Mutex>&  x, shared_lock<Mutex>&  y)
{
    x.swap(y);
}

}  // ting

#endif
